DfsPackFile: Enable/disable object size index via DfsReaderOptions

DfsPackFile always uses the object size index if available. That is
the desired final state, but for a safe rollout, we should be able to
disable using the object size index.

Add an option (dfs.useObjectSizeIndex) to enable/disable the usage of
the object size index. False by default.

This changes the default from true to false. It only makes a different
for the DFS stack when writing of the index was explicitely
enabled. This is an optimization, so it shouldn't cause any
regression. Operators can restore previous behaviour setting
"dfs.useObjectSizeIndex" to true.

Change-Id: I44bf5a57e3942a4ecfe66d58bfa9175e99f96fcc

3 files changed, 37 insertions, 0 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java
index 3e4d4d300c..b94a84a41c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackFile.java
@@ -354,6 +354,7 @@ public final class DfsPackFile extends BlockBasedFile {
 		}
 
 		if (objectSizeIndexLoadAttempted
+				|| !ctx.getOptions().shouldUseObjectSizeIndex()
 				|| !desc.hasFileExt(OBJECT_SIZE_INDEX)) {
 			// Pack doesn't have object size index
 			return null;
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReaderOptions.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReaderOptions.java
index f2ac461deb..5f5e81977b 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReaderOptions.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReaderOptions.java
@@ -15,6 +15,7 @@ import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_DFS_SECTION;
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_DELTA_BASE_CACHE_LIMIT;
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_STREAM_BUFFER;
 import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_STREAM_FILE_THRESHOLD;
+import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_USE_OBJECT_SIZE_INDEX;
 
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.storage.pack.PackConfig;
@@ -36,6 +37,8 @@ public class DfsReaderOptions {
 
 	private boolean loadRevIndexInParallel;
 
+	private boolean useObjectSizeIndex;
+
 	/**
 	 * Create a default reader configuration.
 	 */
@@ -137,6 +140,28 @@ public class DfsReaderOptions {
 	}
 
 	/**
+	 * Use the object size index if available.
+	 *
+	 * @return true if the reader should try to use the object size index. if
+	 *         false, the reader ignores that index.
+	 */
+	public boolean shouldUseObjectSizeIndex() {
+		return useObjectSizeIndex;
+	}
+
+	/**
+	 * Set if the reader should try to use the object size index
+	 *
+	 * @param useObjectSizeIndex true to use it, false to ignore the object size index
+	 *
+	 * @return {@code this}
+	 */
+	public DfsReaderOptions setUseObjectSizeIndex(boolean useObjectSizeIndex) {
+		this.useObjectSizeIndex = useObjectSizeIndex;
+		return this;
+	}
+
+	/**
 	 * Update properties by setting fields from the configuration.
 	 * <p>
 	 * If a property is not defined in the configuration, then it is left
@@ -168,6 +193,10 @@ public class DfsReaderOptions {
 				CONFIG_DFS_SECTION,
 				CONFIG_KEY_STREAM_BUFFER,
 				getStreamPackBufferSize()));
+
+		setUseObjectSizeIndex(rc.getBoolean(CONFIG_CORE_SECTION,
+				CONFIG_DFS_SECTION, CONFIG_KEY_USE_OBJECT_SIZE_INDEX,
+				false));
 		return this;
 	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
index 0edf3c5ad0..e9fbc65696 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
@@ -1012,4 +1012,11 @@ public final class ConfigConstants {
 	 * @since 6.7
 	 */
 	public static final String CONFIG_KEY_READ_CHANGED_PATHS = "readChangedPaths";
+
+	/**
+	 * The "useObjectSizeIndex" key
+	 *
+	 * @since 7.0
+	 */
+	public static final String CONFIG_KEY_USE_OBJECT_SIZE_INDEX = "useObjectSizeIndex";
 }